Front with Heavy Rainfalls in the Asian Subtropical Humid Region in a 6-Level 77 km-Mesh Primitive Equation Model

Abstract

Real data forecast experiments of heavy rainfalls in Baiu front (a front in the Asian subtropical humid region) are made for two typical cases by using a 6-level 77km-mesh regional primitive equation model.
We show first that the moist convective adjustment scheme which has bcen used in coarse-mesh models is not always suitable for the present model as the scheme tends to produce heavy rainfalls in the area far south to the frontal zone. In order to confine heavy rainfalls within the frontal zone or in the vicinity of frontal disturbances, we improved the scheme by controling the adjustment through low-level vorticity and by modifying the critical lapse rate used in the scheme.
Detailed analysis is made for two cases of Baiu frontal heavy rainfalls predicted by the model including the improved adjustment scheme. The characteristic features of Baiu front associated with heavy rainfalls (i.e., concentration of heavy rainfalls in a zone to the south of subtropical jet stream, formation of a low-level strong wind zone to the south of the heavy rainfall zone, moist tongue and a zone of convective warming in the middle
troposphere) are accurately predicted.